In the past, as a system of auto focus (AF) function of electronic devices, such as a digital camera on which an image sensor is mounted, an image-plane phase-difference AF has been known (for example, see Patent Literature 1). For an image sensor actualizing an image-plane phase-difference AF, a phase difference detection pixel for pupil-dividing incident light is arranged at a predetermined positon, in addition to a normal pixel for obtaining a pixel signal of an image.
A past phase difference detection pixel has a metal light shielding film with an opening that is shifted relative to the optical axis of an on-chip lens and is formed between the on-chip lens and PD, and is used only for an application of phase difference detection. Accordingly, in a case where a past phase difference detection pixel is arranged in an image sensor, a pixel signal used for an image cannot be obtained from the position.
Consequently, a structure in which one on-chip lens is shared by a plurality of PDs is proposed as a structure of a pixel whose output can be used not only for an application of phase difference detection but also for an application of pixel signal detection.
FIG. 1 shows a structure in which one on-chip lens 1 is shared by PD 2L and PD 2R that are laid out laterally, as an example of a structure in which one on-chip lens is shared by a plurality of PDs for the same color (that are covered with color filters of the same color or have sensitivity for the same color).
According to an image sensor in which pixels having such a structure are arranged, in a case where outputs from a plurality of PDs sharing one on-chip lens are added and used, it can be utilized as a pixel signal, and, in a case where the outputs from a plurality of PDs are used individually, it can be utilized for object trimming, dimension measurement, 3D data acquisition, refocusing and the like in addition to image-plane phase-difference AF.
However, in a case of a structure in which two PDs (PD 2L and PD 2R) share the on-chip lens 1 as shown in FIG. 1, if an object is out of focus, sensitivity difference is generated between the PD 2L and PD 2R. As the result, as shown in FIG. 2, there is a problem that nearity of the addition signal of both gets out of shape after the saturation of one of PD 2L and PD 2R. Meanwhile, L (Left) and R (Right) in FIG. 2 mean, respectively, charges that are generated in PD 2L and in RD 2R. The same is applied to subsequent drawings.
Consequently, according to an embodiment of the present disclosure, such a structure is adopted that a barrier between PD 2L and PD 2R is set to be low and, in a case where one of PD 2L and PD 2R is saturated, saturated charges flow out to the other, as shown in FIG. 3. This makes it possible to keep nearity of the addition signal of both even in a case where one of PD 2L and PD 2R has been saturated, as shown in FIG. 4.